package com.demo2do.core.utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.net.URL;
import java.net.URLDecoder;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * <p>
 * ClasspathScanner is used to locate classes that are available in the/a class
 * path and meet arbitrary conditions. The two most common conditions are that a
 * class implements/extends another class, or that is it annotated with a
 * specific annotation. However, through the use of the {@link Test} class it is
 * possible to search using arbitrary conditions.
 * </p>
 * 
 * <p>
 * A ClassLoader is used to locate all locations (directories and jar files) in
 * the class path that contain classes within certain packages, and then to load
 * those classes and check them. By default the ClassLoader returned by
 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
 * be overridden by calling {@link #setClassLoader(ClassLoader)} prior to
 * invoking any of the {@code find()} methods.
 * </p>
 * 
 * <p>
 * General searches are initiated by calling the
 * {@link #find(ClasspathScanner.Test, String...)} ()} method and supplying a
 * package name and a Test instance. This will cause the named package <b>and
 * all sub-packages</b> to be scanned for classes that meet the test. There are
 * also utility methods for the common use cases of scanning multiple packages
 * for extensions of particular classes, or classes annotated with a specific
 * annotation.
 * </p>
 * 
 * <p>
 * The standard usage pattern for this class is as follows:
 * </p>
 * 
 * <pre>
 * ClasspathScanner&lt;ActionBean&gt; resolver = new ClasspathScanner&lt;ActionBean&gt;();
 * resolver.findImplementation(ActionBean.class, pkg1, pkg2);
 * resolver.find(new CustomTest(), pkg1);
 * resolver.find(new CustomTest(), pkg2);
 * Collection&lt;ActionBean&gt; beans = resolver.getClasses();
 * </pre>
 * 
 * <p>
 * This class was copied from Stripes -
 * http://stripes.mc4j.org/confluence/display/stripes/Home
 * </p>
 * 
 * @author Downpour
 */
public class ClasspathScanner<T> {

	private static final Log logger = LogFactory.getLog(ClasspathScanner.class);

	/**
	 * A simple interface that specifies how to test classes to determine if
	 * they are to be included in the results produced by the ResolverUtil.
	 */
	public static interface Test {
		/**
		 * Will be called repeatedly with candidate classes. Must return True if
		 * a class is to be included in the results, false otherwise.
		 */
		boolean matches(Class<?> type);

		boolean matches(URL resource);

		boolean doesMatchClass();

		boolean doesMatchResource();
	}

	public static abstract class ClassTest implements Test {
		public boolean matches(URL resource) {
			throw new UnsupportedOperationException();
		}

		public boolean doesMatchClass() {
			return true;
		}

		public boolean doesMatchResource() {
			return false;
		}
	}

	public static abstract class ResourceTest implements Test {
		public boolean matches(Class<?> cls) {
			throw new UnsupportedOperationException();
		}

		public boolean doesMatchClass() {
			return false;
		}

		public boolean doesMatchResource() {
			return true;
		}
	}

	/**
	 * A Test that checks to see if each class is assignable to the provided
	 * class. Note that this test will match the parent type itself if it is
	 * presented for matching.
	 */
	public static class IsA extends ClassTest {
		private Class<?> parent;

		/**
		 * Constructs an IsA test using the supplied Class as the parent
		 * class/interface.
		 */
		public IsA(Class<?> parentType) {
			this.parent = parentType;
		}

		/**
		 * Returns true if type is assignable to the parent type supplied in the
		 * constructor.
		 */
		public boolean matches(Class<?> type) {
			return type != null && parent.isAssignableFrom(type);
		}

		@Override
		public String toString() {
			return "is assignable to " + parent.getSimpleName();
		}
	}

	/**
	 * A Test that checks to see if each class name ends with the provided
	 * suffix.
	 */
	public static class NameEndsWith extends ClassTest {
		private String suffix;

		/** Constructs a NameEndsWith test using the supplied suffix. */
		public NameEndsWith(String suffix) {
			this.suffix = suffix;
		}

		/**
		 * Returns true if type name ends with the suffix supplied in the
		 * constructor.
		 */
		public boolean matches(Class<?> type) {
			return type != null && type.getName().endsWith(suffix);
		}

		@Override
		public String toString() {
			return "ends with the suffix " + suffix;
		}
	}

	/**
	 * A Test that checks to see if each class is annotated with a specific
	 * annotation. If it is, then the test returns true, otherwise false.
	 */
	public static class AnnotatedWith extends ClassTest {
		private Class<? extends Annotation> annotation;

		/** Construts an AnnotatedWith test for the specified annotation type. */
		public AnnotatedWith(Class<? extends Annotation> annotation) {
			this.annotation = annotation;
		}

		/**
		 * Returns true if the type is annotated with the class provided to the
		 * constructor.
		 */
		public boolean matches(Class<?> type) {
			return type != null && type.isAnnotationPresent(annotation);
		}

		@Override
		public String toString() {
			return "annotated with @" + annotation.getSimpleName();
		}
	}

	public static class NameIs extends ResourceTest {
		private String name;

		public NameIs(String name) {
			this.name = "/" + name;
		}

		public boolean matches(URL resource) {
			return (resource.getPath().endsWith(name));
		}

		@Override
		public String toString() {
			return "named " + name;
		}
	}

	/** The set of matches being accumulated. */
	private Set<Class<? extends T>> classMatches = new HashSet<Class<? extends T>>();

	/** The set of matches being accumulated. */
	private Set<URL> resourceMatches = new HashSet<URL>();

	/**
	 * The ClassLoader to use when looking for classes. If null then the
	 * ClassLoader returned by Thread.currentThread().getContextClassLoader()
	 * will be used.
	 */
	private ClassLoader classloader;

	/**
	 * Provides access to the classes discovered so far. If no calls have been
	 * made to any of the {@code find()} methods, this set will be empty.
	 * 
	 * @return the set of classes that have been discovered.
	 */
	public Set<Class<? extends T>> getClasses() {
		return classMatches;
	}

	public Set<URL> getResources() {
		return resourceMatches;
	}

	/**
	 * Returns the classloader that will be used for scanning for classes. If no
	 * explicit ClassLoader has been set by the calling, the context class
	 * loader will be used.
	 * 
	 * @return the ClassLoader that will be used to scan for classes
	 */
	public ClassLoader getClassLoader() {
		return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader;
	}

	/**
	 * Sets an explicit ClassLoader that should be used when scanning for
	 * classes. If none is set then the context classloader will be used.
	 * 
	 * @param classloader
	 *            a ClassLoader to use when scanning for classes
	 */
	public void setClassLoader(ClassLoader classloader) {
		this.classloader = classloader;
	}

	/**
	 * Attempts to discover classes that are assignable to the type provided. In
	 * the case that an interface is provided this method will collect
	 * implementations. In the case of a non-interface class, subclasses will be
	 * collected. Accumulated classes can be accessed by calling
	 * {@link #getClasses()}.
	 * 
	 * @param parent
	 *            the class of interface to find subclasses or implementations
	 *            of
	 * @param packageNames
	 *            one or more package names to scan (including subpackages) for
	 *            classes
	 */
	public void findImplementations(Class<?> parent, String... packageNames) {
		if (packageNames == null)
			return;

		Test test = new IsA(parent);
		for (String pkg : packageNames) {
			findInPackage(test, pkg);
		}
	}

	/**
	 * Attempts to discover classes who's name ends with the provided suffix.
	 * Accumulated classes can be accessed by calling {@link #getClasses()}.
	 * 
	 * @param suffix
	 *            The class name suffix to match
	 * @param packageNames
	 *            one or more package names to scan (including subpackages) for
	 *            classes
	 */
	public void findSuffix(String suffix, String... packageNames) {
		if (packageNames == null)
			return;

		Test test = new NameEndsWith(suffix);
		for (String pkg : packageNames) {
			findInPackage(test, pkg);
		}
	}

	/**
	 * Attempts to discover classes that are annotated with to the annotation.
	 * Accumulated classes can be accessed by calling {@link #getClasses()}.
	 * 
	 * @param annotation
	 *            the annotation that should be present on matching classes
	 * @param packageNames
	 *            one or more package names to scan (including subpackages) for
	 *            classes
	 */
	public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
		if (packageNames == null)
			return;

		Test test = new AnnotatedWith(annotation);
		for (String pkg : packageNames) {
			findInPackage(test, pkg);
		}
	}

	public void findNamedResource(String name, String... pathNames) {
		if (pathNames == null)
			return;

		Test test = new NameIs(name);
		for (String pkg : pathNames) {
			findInPackage(test, pkg);
		}
	}

	/**
	 * Attempts to discover classes that pass the test. Accumulated classes can
	 * be accessed by calling {@link #getClasses()}.
	 * 
	 * @param test
	 *            the test to determine matching classes
	 * @param packageNames
	 *            one or more package names to scan (including subpackages) for
	 *            classes
	 */
	public void find(Test test, String... packageNames) {
		if (packageNames == null)
			return;

		for (String pkg : packageNames) {
			findInPackage(test, pkg);
		}
	}

	/**
	 * Scans for classes starting at the package provided and descending into
	 * subpackages. Each class is offered up to the Test as it is discovered,
	 * and if the Test returns true the class is retained. Accumulated classes
	 * can be fetched by calling {@link #getClasses()}.
	 * 
	 * @param test
	 *            an instance of {@link Test} that will be used to filter
	 *            classes
	 * @param packageName
	 *            the name of the package from which to start scanning for
	 *            classes, e.g. {@code net.sourceforge.stripes}
	 */
	public void findInPackage(Test test, String packageName) {
		packageName = packageName.replace('.', '/');
		ClassLoader loader = getClassLoader();
		Enumeration<URL> urls;

		try {
			urls = loader.getResources(packageName);
		} catch (IOException ioe) {
			if (logger.isWarnEnabled()) {
				logger.warn("Could not read package: " + packageName, ioe);
			}
			return;
		}

		while (urls.hasMoreElements()) {
			try {
				String urlPath = urls.nextElement().getFile();
				urlPath = URLDecoder.decode(urlPath, "UTF-8");

				// If it's a file in a directory, trim the stupid file: spec
				if (urlPath.startsWith("file:")) {
					urlPath = urlPath.substring(5);
				}

				// Else it's in a JAR, grab the path to the jar
				if (urlPath.indexOf('!') > 0) {
					urlPath = urlPath.substring(0, urlPath.indexOf('!'));
				}

				if (logger.isInfoEnabled()) {
					logger.info("Scanning for classes in [" + urlPath + "] matching criteria: " + test);
				}
				File file = new File(urlPath);
				if (file.isDirectory()) {
					loadImplementationsInDirectory(test, packageName, file);
				} else {
					loadImplementationsInJar(test, packageName, file);
				}
			} catch (IOException ioe) {
				if (logger.isWarnEnabled()) {
					logger.warn("could not read entries", ioe);
				}
			}
		}
	}

	/**
	 * Finds matches in a physical directory on a filesystem. Examines all files
	 * within a directory - if the File object is not a directory, and ends with
	 * <i>.class</i> the file is loaded and tested to see if it is acceptable
	 * according to the Test. Operates recursively to find classes within a
	 * folder structure matching the package structure.
	 * 
	 * @param test
	 *            a Test used to filter the classes that are discovered
	 * @param parent
	 *            the package name up to this directory in the package
	 *            hierarchy. E.g. if /classes is in the classpath and we wish to
	 *            examine files in /classes/org/apache then the values of
	 *            <i>parent</i> would be <i>org/apache</i>
	 * @param location
	 *            a File object representing a directory
	 */
	private void loadImplementationsInDirectory(Test test, String parent, File location) {
		File[] files = location.listFiles();
		StringBuilder builder = null;

		for (File file : files) {
			builder = new StringBuilder(100);
			builder.append(parent).append("/").append(file.getName());
			String packageOrClass = (parent == null ? file.getName() : builder.toString());

			if (file.isDirectory()) {
				loadImplementationsInDirectory(test, packageOrClass, file);
			} else if (isTestApplicable(test, file.getName())) {
				addIfMatching(test, packageOrClass);
			}
		}
	}

	private boolean isTestApplicable(Test test, String path) {
		return test.doesMatchResource() || path.endsWith(".class") && test.doesMatchClass();
	}

	/**
	 * Finds matching classes within a jar files that contains a folder
	 * structure matching the package structure. If the File is not a JarFile or
	 * does not exist a warning will be logged, but no error will be raised.
	 * 
	 * @param test
	 *            a Test used to filter the classes that are discovered
	 * @param parent
	 *            the parent package under which classes must be in order to be
	 *            considered
	 * @param jarfile
	 *            the jar file to be examined for classes
	 */
	@SuppressWarnings("resource")
	private void loadImplementationsInJar(Test test, String parent, File jarfile) {

		try {
			JarEntry entry;
			JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile));

			while ((entry = jarStream.getNextJarEntry()) != null) {
				String name = entry.getName();
				if (!entry.isDirectory() && name.startsWith(parent) && isTestApplicable(test, name)) {
					addIfMatching(test, name);
				}
			}
		} catch (IOException ioe) {
			logger.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test + " due to an IOException", ioe);
		}
	}

	/**
	 * Add the class designated by the fully qualified class name provided to
	 * the set of resolved classes if and only if it is approved by the Test
	 * supplied.
	 * 
	 * @param test
	 *            the test used to determine if the class matches
	 * @param fqn
	 *            the fully qualified name of a class
	 */
	@SuppressWarnings({ "rawtypes", "unchecked" })
	protected void addIfMatching(Test test, String fqn) {
		try {
			ClassLoader loader = getClassLoader();
			if (test.doesMatchClass()) {
				String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
				if (logger.isDebugEnabled()) {
					logger.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]");
				}

				Class type = loader.loadClass(externalName);
				if (test.matches(type)) {
					classMatches.add((Class<T>) type);
				}
			}
			if (test.doesMatchResource()) {
				URL url = loader.getResource(fqn);
				if (url == null) {
					url = loader.getResource(fqn.substring(1));
				}
				if (url != null && test.matches(url)) {
					resourceMatches.add(url);
				}
			}
		} catch (Throwable t) {
			if (logger.isWarnEnabled()) {
				logger.warn("Could not examine class '" + fqn + "' due to a " + t.getClass().getName() + " with message: " + t.getMessage());
			}
		}
	}
}